In the world of heavy duty equipment, mining, trenching and road milling equipment needs to be built to take the strain and wear of removing asphalt, concrete, rock, minerals, coal and the like from the earth's surface and subterrain.
Generally, some very hard material, such as tungsten carbide and lately industrial and man-made diamond material provide the leading edge of such heavy duty equipment. In road milling, the surface removing equipment includes a rotatable drum on which a plurality of bit assemblies, including the aforementioned very hard material tips, are positioned in close proximity, usually in spiral or chevron shape, on the outside of a rotatable drum.
Prior to applicant's ground-breaking inventions found in U.S. Pat. Nos. 6,371,567 and 6,585,326, the very hard tips, found in what is termed “bits” were rotatably mounted on bit holders, or intermediate parts, that were fastened to base blocks which, in turn, were mounted on the outside of such drums, or on the outside of plates positioned on the outside of heavy duty connected links. The intermediate parts or bit holders were retained on the base blocks by bolting or by use of other retainer distal end means. Applicant's prior inventions eliminated the need for the nuts at the back end of the base blocks by providing a bit holder having a hollow slotted shank with an increased overall super interference fit being driven and holding same securely against the base block bore.
Especially with road milling machines and other heavy duty equipment having established configurations, the need for new and improved material removing assemblies at the point of their contact with the material to be removed, has necessitated that the equipment, even if improved, be largely interchangeably compatible.
With traditional bit holders having generally cylindrical shanks nominally 1½ inches in diameter and about 2½ inches in length to fit into previously existing base block bores, applicant's improved interference fit bit holders had similar diameter and length shanks.
Given the heavy duty nature of highway milling and material removal, the ability to drive in both bit holders having removable bits mounted therein, and also unitary combination bit/bit holders that include either industrial diamonds or PCD material at the tips thereof into base blocks and retain them therein is highly desirable. In this regard, improved access to the rear of base blocks for punching out bits and combination unitary bit/holders from their mounted position in the base blocks would be very desirable.
A need has arisen for base blocks having shorter length bit holder bores and, consequently, improved bit holders and combination unitary bit/holders having shortened shanks thereon which matingly engage and are retained in such base block bores.